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A wrecking ball is a large steel sphere used to demolish structures. The majority of wrecking balls are made through a pressure forging process that hardens the steel while it is still cooling. Hard steel wrecking balls are capable of crashing through most concrete and brick buildings. They are generally suspended from a crane or other tall construction equipment using thick steel cable. Movement from the equipment swings the wrecking ball to strike the desired location with sufficient force for demolition.
Modern versions of wrecking balls have evolved to be slightly pear-shaped. Completely round wrecking balls, like the ones shown in cartoons, have a tendency to get stuck when they are pulled back from wreckage. Other shapes were tested by manufacturers to find a better wrecking ball solution. Demolition crews found that the graduated spherical wrecking ball form slid out of the holes it had created much more easily. Many size variations of the modern design are available, but the iconic round steel wrecking balls are becoming increasingly difficult to find.
Skilled, trained and licensed demolition professionals operate the controls that hurtle these huge masses of steel into the sides of structures. Weeks and even months of planning go into the process of preparing and clearing each new site for demolition. The wrecking ball does not start to swing until the crew is ready and the all-clear signal is given.
Despite their weight, wrecking balls are ineffective without momentum generated kinetic energy. Momentum is product of the ball's mass and velocity, or directional speed. As the wrecking ball swings further from the point of equilibrium where the cable is perpendicular to the ground, the momentum gradually increases. Machinery operators typically build up momentum with several free swings before the ball makes each contact with the structure. Longer steel cables allow a freer swing, resulting in powerfully destructive momentum.
Project cost, noise restrictions, and time constraints in the modern demolition industry have effectively sidelined the steel wrecking ball. Knocking down a large structure in this manner takes a skilled operator several hours at the controls. Newer demolition technologies are quicker, more precise, and less expensive. Advances in controlled explosives and powerful hydraulic excavators have made the more traditional wrecking ball the less efficient option. Occasionally, wrecking balls are brought in to weaken a building's framework just enough for the excavators to finish pulling it down.
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